Inductive coupler for power line communications

ABSTRACT

There is provided an inductive coupler for coupling a signal to a conductor. The inductive coupler includes (a) a magnetic core having an aperture through which the conductor is routed, (b) a winding wound around a portion of the magnetic core, where the signal is coupled between the winding and the conductor via the magnetic core, and (c) an electrically insulating, compressible material situated between the winding and the magnetic core, having a hardness of between about 10 and about 100 on a hardness type shore A durometer scale.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 11/133,671, filed May 20, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to power line communications, and moreparticularly, to a configuration of a data coupler for power linecommunications.

2. Description of the Related Art

Power line communications (PLC), also known as broadband over power line(BPL), is a technology that encompasses transmission of data at highfrequencies through existing electric power lines, i.e., conductors usedfor carrying a power current. A data coupler for power linecommunications couples a data signal between a power line and acommunication device such as a modem.

An example of such a data coupler is an inductive coupler that includesa set of cores, and a winding wound around a portion of the cores. Theinductive coupler operates as a transformer, where the cores aresituated on a power line such that the power line serves as a primarywinding of the transformer, and the winding of the inductive coupler isa secondary winding of the transformer.

The cores are typically constructed with magnetic materials, such asferrites, powdered metal, or nano-crystalline material. The cores areelectrified by contact with the power line and require insulation fromthe secondary winding. Typically, insulation is provided between thecores and secondary winding by embedding both the cores and thesecondary winding in electrically insulating material, such as epoxy.During a molding process, the electrically insulating material reachesan elevated temperature. As the electrically insulating material, in aliquid state, flows around the cores, it begins to cool and contract.The thermal coefficient of expansion of the electrically insulatingmaterial is typically much higher than that of the core, andconsequently, stress cracking of the electrically insulating materialmay occur during a transition from liquid to solid state.

In field operation, stiffly held magnetic cores made of brittle materialmay crack due to vibration or thermal expansion. There is a need for aninductive coupler configured to avoid such cracking.

SUMMARY OF THE INVENTION

There is provided an inductive coupler for coupling a signal to aconductor. The inductive coupler includes (a) a magnetic core having anaperture through which the conductor is routed, (b) a winding woundaround a portion of the magnetic core, where the signal is coupledbetween the winding and the conductor via the magnetic core, (c) anelectrically insulating material situated between the winding and themagnetic core, having a hardness of between about 10 and about 100 on ahardness type shore A durometer scale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front and cross-sectional view of an inductive coupler on apower line.

FIG. 2 is a cross-sectional view of an upper and a lower core of aninductive coupler, with compressible layers around the cores.

FIG. 3 is a cross-sectional view of an upper and a lower core of aninductive coupler with compressible layers that expose the core faces.

FIG. 4 is a cross-sectional view of an upper and a lower core of aninductive coupler, with insulation serving as a compressible layeraround the cores.

DESCRIPTION OF THE INVENTION

In a PLC system, power current is typically transmitted through a powerline at a frequency in the range of 50–60 hertz (Hz). In a low voltageline, power current is transmitted with a voltage between about 90 to600 volts, and in a medium voltage line, power current is transmittedwith a voltage between about 2,400 volts to 35,000 volts. The frequencyof the data signals is greater than or equal to about 1 megahertz (MHz),and the voltage of the data signal ranges from a fraction of a volt to afew tens of volts.

FIG. 1 is an illustration of a front view with internal componentsvisible with dashed lines, and a cross-section view, of an inductivecoupler 100 on a conductor, i.e., power line 110. Inductive coupler 100has a split magnetic core configured of an upper core 120 and a lowercore 125 that are shaped such that when they are placed adjacent to oneanother, they provide an aperture 105 through which power line 110 isrouted. Inductive coupler 100 also has a winding 130 wound around aportion of lower core 125. Winding 130 is for connection with a modem orother communications equipment (not shown). In FIG. 1, winding 130 isshown as being wound once around lower core 125, but in practice,winding 130 may be wound two or more times. A data signal is coupledbetween winding 130 and power line 110 via the split magnetic core.

Upper core 120 is enveloped by a compressible material, configured as aninward layer 140B, an outward layer 140A, an end layer 140C and an endlayer 140D. A layer 150 of an electrically insulating material isdisposed over outward layer 140A, end layer 140C and end layer 140D.

Lower core 125 is enveloped by a compressible material, configured as aninward layer 145B, an outward layer 145A, an end layer 145C and an endlayer 145D. A layer 155 of an electrically insulating material is moldedinto a three-dimensional shape and disposed over inward layer 145B,outward layer 145A, end layer 140C and end layer 140D. Layer 155 alsoenvelopes the portion of winding 130 that is wound around core 125. Incross-sectional views of FIGS. 1–3, layer 155 is represented as having aportion 155A disposed over outward layer 145A, and a portion 155Bdisposed over inward layer 145B

The compressible material of inward layer 140B, outward layer 140A, endlayer 140C and end layer 140D has a hardness that is less than that ofthe electrically insulating material of layer 150. Outward layer 140A,end layer 140C and end layer 140D compress as layer 150 cures, cools andcontracts during a molding process. Such compression obviates crackingof layer 150 during a cooling phase. Furthermore, outward layer 140A,inward layer 140B, end layer 140C and end layer 140D provide anenvironmental seal for upper core 120.

The compressible material of outward layer 145A, inward layer 145B, endlayer 145C and end layer 145D has a hardness that is less than that ofthe electrically insulating material of layer 155. Outward layer 145A,inward layer 145B, end layer 145C and end layer 145D compress as layer155 cures, cools and contracts during a molding process. Suchcompression obviates cracking of layer 155 during a cooling phase.Outward layer 145A, inward layer 145B, end layer 145C and end layer 145Dalso provide an environmental seal for lower core 125.

The compressible material of outward layers 140A and 145A, inward layers140B and 145B, and end layers 140C, 140D, 145C and 145D preferably has ahardness of between about 10 and about 100 on a hardness type shore Adurometer scale. An example of such a material is Ethylene PropyleneDiene Monomer (EPDM). Hardness testing procedures are provided by theAmerican Society for Testing & Materials, ASTM D2240-03.

In practical operation, inductive coupler 100 may be subjected to avariety of temperatures and environmental conditions, for example,summer heat, winter cold, rain, snow and ice. Because of a differencebetween thermal coefficients of expansion of upper core 120 and layer150, a gap may tend to develop between upper core 120 and layer 150.Water could accumulate in the gap, thereafter freezing and expanding,i.e., frost heave, further aggravating the gap, and resulting in cracksin both upper core 120 and layer 150. Such gaps and cracks in inductivecoupler 100 could lead to electric discharge, causing radio frequencynoise, which is detrimental to the operation of a power linecommunications system. Electric discharge may also cause a deteriorationof the electrically insulating material of layer 150, over time, and maylead to insulation failure. Outward layer 140A, end layer 140C and endlayer 140D seal such gaps and cracks, and thus reduce opportunities fordischarges to occur. Additionally, outward layer 140A, inward layer140B, end layer 140C and end layer 140D absorb physical shock andvibration that could damage upper core 120. Outward layer 145A, inwardlayer 145B, end layer 145C and end layer 145D provide similar benefitswith regard to layer 155 and lower core 125.

The compressible material of outward layers 140A and 145A, inward layers140B and 145B, and end layers 140C, 140D, 145C and 145D, also,preferably, has a semi-conductive electrical property. Thus, each ofoutward layers 140A and 145A, and inward layers 140B and 145B, whensubjected to an electric charge, distribute the electrical charge overtheir respective volumes, and provide an equipotential volume. In apreferred implementation, a bulk resistivity of outward layers 140A and145A, and inward layers 140B and 145B is between about 5 and about 1000ohm-cm so that a voltage difference between upper core 120 and lowercore 125 will not exceed 2% of a voltage on power line 110.

Outward layer 140A, inward layer 140B, end layer 140C and end layer140D, are in physical and electrical contact with outward layer 145A,inward layer 145B, end layer 145C and end layer 145D. Upper core 120 andlower core 125 are thus connected to one another and are at a commonelectrical potential as one another, minimizing any potential differencethat might cause an electrical discharge between upper core 120 andlower core 125. Outward layers 140A and 145A, inward layers 140B and145B, and end layers 140C, 140D, 145C and 145D collectively form asemi-conducting sheath that minimizes partial discharge or corona ininductive coupler 100.

FIG. 2 is a cross-sectional view of an upper and a lower core of aninductive coupler, with compressible layers around the cores. Upper core120 has a pole face 200 and lower core 125 has a pole face 205. Poleface 200 and pole face 205 are spaced apart from one another by an airgap 210.

The term “air gap” is a term of art that refers to a region, betweenmagnetic cores, having non-magnetic material therein. Air gaps improvemagnetic characteristics of a magnetic circuit at a high current level.

Outward layer 140A, inward layer 140B, and end layers 140C and 140D (notshown in FIG. 2) converge with one another and cover pole face 200.Outward layer 145A, inward layer 145B, and end layers 145C and 145D (notshown in FIG. 2) converge with one another and cover pole face 205.Thus, the layers provide a fill of non-magnetic material for air gap210. This configuration of material in air gap 210 also cushions polefaces 200 and 205 from physical shock and vibration, to reduce anopportunity for fracturing of upper core 120 and lower core 125.

FIG. 3 is a cross-sectional view of an upper and a lower core of aninductive coupler with compressible layers that expose the core faces.Outward layers 140A and 145A, inward layers 140B and 145B, end layers140C, 140D, 145C and 145D (not shown in FIG. 3) terminate at, and do notcover, pole face 220 and 225. However, outward layers 140A and 145A,inward layers 140B and 145B, and end layers 140C, 145C, 140D and 145Dare in contact with one another. Thus, there is electrical continuitybetween outward layers 140A and 145A, inward layers 140B and 145B, andend layers 140C, 145C, 140D and 145D.

FIG. 4 is a cross-sectional view of an upper and a lower core of aninductive coupler, with insulation serving as a compressible layeraround the cores. A layer 400 is disposed on an outward surface of uppercore 120, and disposed on an inward surface and an outward surface oflower core 125. Layer 400 is composed of a material that is bothinsulating and compressible. That is, layer 400 is an insulator and isalso compressible for over-molding of upper core 120 and lower core 125.Preferably, layer 400 has a hardness of between about 10 and about 100on a hardness type shore A durometer scale. Layer 400 can be composed ofa silicone, for example.

The techniques described herein are exemplary, and should not beconstrued as implying any particular limitation on the presentinvention. It should be understood that various alternatives,combinations and modifications could be devised by those skilled in theart. The present invention is intended to embrace all such alternatives,modifications and variances that fall within the scope of the appendedclaims.

1. An inductive coupler for coupling a signal to a conductor,comprising: a magnetic core having an aperture through which saidconductor is routed; a winding wound around a portion of said magneticcore, wherein said signal is coupled between said winding and saidconductor via said magnetic core; and an electrically insulatingcompressible material situated between said winding and said magneticcore, having a hardness of between about 10 and about 100 on a hardnesstype shore A durometer scale.
 2. The inductive coupler of claim 1,further comprising an electrically insulating material on an outwardsurface of said magnetic core, having a hardness of between about 10 andabout 100 on a hardness type shore A durometer scale.